Evaluate
3\left(x-2y\right)\left(x+12y\right)
Expand
3x^{2}+30xy-72y^{2}
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4x^{2}+12xy+9y^{2}-\left(x-9y\right)^{2}
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(2x+3y\right)^{2}.
4x^{2}+12xy+9y^{2}-\left(x^{2}-18xy+81y^{2}\right)
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(x-9y\right)^{2}.
4x^{2}+12xy+9y^{2}-x^{2}+18xy-81y^{2}
To find the opposite of x^{2}-18xy+81y^{2}, find the opposite of each term.
3x^{2}+12xy+9y^{2}+18xy-81y^{2}
Combine 4x^{2} and -x^{2} to get 3x^{2}.
3x^{2}+30xy+9y^{2}-81y^{2}
Combine 12xy and 18xy to get 30xy.
3x^{2}+30xy-72y^{2}
Combine 9y^{2} and -81y^{2} to get -72y^{2}.
4x^{2}+12xy+9y^{2}-\left(x-9y\right)^{2}
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(2x+3y\right)^{2}.
4x^{2}+12xy+9y^{2}-\left(x^{2}-18xy+81y^{2}\right)
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(x-9y\right)^{2}.
4x^{2}+12xy+9y^{2}-x^{2}+18xy-81y^{2}
To find the opposite of x^{2}-18xy+81y^{2}, find the opposite of each term.
3x^{2}+12xy+9y^{2}+18xy-81y^{2}
Combine 4x^{2} and -x^{2} to get 3x^{2}.
3x^{2}+30xy+9y^{2}-81y^{2}
Combine 12xy and 18xy to get 30xy.
3x^{2}+30xy-72y^{2}
Combine 9y^{2} and -81y^{2} to get -72y^{2}.
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